1. Field of the Invention
The present invention relates to a method and an apparatus for dissolving gases into liquid phases under high pressure, ranging from 2 to 7 atmospheric pressure, and high rotation velocity (2,500 rpm or higher) in an enclosed pressure vessel, and for subsequently releasing the pressurized liquid into an open vessel in order to generate extremely fine micro bubbles with a diameter less than 80 microns. Conventional bubble separation, recarbonation, aeration, and ozonation technologies have a low efficiency for gas dissolution and require a long retention time, and large reactors. Conventional biological oxidation processes involve the use of coarse air or oxygen bubbles which are inefficient and cause air pollution. The present invention represents a highly efficient alternative to conventional physical-chemical liquid treatment methods such as conventional bubble separation, flotation, recarbonation, aeration, ozonation, chlorination, oxygenation, etc. The present invention is also an alternative to conventional biological oxidation processes, such as conventional activated sludge, trickling filter, rotating biological contactors, biological tower, deep shaft process, biological fluidized bed, etc.
The adsorptive bubble separation process (including dissolved air flotation, dispersed air flotation, froth flotation, etc.) is a very effective technology for solid-liquid separation and has been in use outside the environmental engineering field for more than 50 years. Originally applied in the field of mining engineering, adsorptive bubble separation now provides the means for separation and/or concentration of 95 percent of the world's base metals and other mineral compounds. Recently, the adsorptive bubble separation process has become increasingly important in such diverse applications as the separation of algaes, seeds, or bacteria from biological reactors, removal of ink from repulped paper stock, recovery of wool fat from food processing streams, peas from pea pods, coal from slate, gluten from starch, oils from industrial effluents, and more recently in drinking water, cooling water, wastewater, and sludge treatments.
Adsorptive bubble separation process may be defined as the mass transfer of a solid from the body of a liquid, to the liquid surface by means of bubble attachment. The solids are in dissolved, suspended and/or colloidal forms. The three basic mechanisms involved are bubble formation, bubble attachment and solids separation. In general, the light weight suspended solids, such as fibers, activated sludge, free oil, chemical flocs, fats, etc., can be readily separated by the process in accordance with physical-chemical bubble attachment mechanism. The colloidal solids, soluble organics, soluble inorganics, and surface active substances are separated from the bulk liquid by the bubble separation process after they are converted from colloidal or soluble form into insoluble form (i.e. suspended solids) which can then be floated by bubbles.
Alternatively, the soluble surface active substances can be separated easily by an adsorptive bubble separation process in accordance with surface adsorption phenomena. Nonsurface active suspended solids, colloidal solids, soluble organics and soluble inorganics can all be converted into surface active substances. All surface active substances in either soluble form or insoluble form can be effectively floated by fine gas bubbles. Production of fine gas bubbles for bubble separation is a difficult engineering task. Conventional methods and apparatus for the production of fine bubbles is similar to an inefficient pressure spray can, which requires over 2 minutes of detention time and over 50 psig pressure. A high horsepower gas compressor for gas dissolving is a necessity for the conventional gas dissolving system.
Conventional recarbonation, aeration and ozonation processes all involve the use of inefficient porous plates or gas diffusers for the introduction of carbon dioxide gas, air or ozone gas into an aqueous phase under atmospheric pressure and low liquid gravimetric pressure. Since bubble sizes are big and non-uniform, many gas bubbles are not able to completely dissolve into the aqueous phase and, therefore, wasted in the gas stream. In cases where ozone gas is used, the residual ozone gas in the gas stream may create an air pollution problem.
The present invention is an enclosed highly efficient pressure vessel, which is specifically designed to dissolve air, oxygen, nitrogen, carbon dioxide, ozone, other gases, or combinations thereof into a liquid stream, such as water, under high pressure (2 to 7 atmospheric pressure) and high rotation velocity (over 2,500 rpm). The swirling flow pattern, special nozzles, and porous gas dissolving means combine to achieve 100 percent gas dissolution in liquid and in turn eliminate the problem of a waste gas stream. The detention time needed for gas dissolving is reduced to a few seconds, therefore, the required size of the gas dissolving pressure vessel is significantly reduced. With the new system, a gas compressor becomes a supplemental means for the enhancement of gas dissolving and is no longer absolutely required. The present invention also relates an improved pressurized water release unit. The pressure vessel's effluent is discharged into a tank through the pressurized water release unit which is equipped with a pressure reduction means for successful generation of extremely fine gas bubbles with diameters less than 80 microns in the liquid of an open vessel. Furthermore, the present invention relates newly improved water purification systems and wastewater treatment systems in which the gas dissolving/releasing apparatus is fully utilized, and to which chemicals and/or microorganisms are dosed for chemical or biochemical reactions.
2. Description of the Prior Art
The method of dissolving volumetric gases into the liquid stream through a liquid-gas mixing vessel of porous gas diffusion tubes, nozzles, porous gas diffusion plates, or mechanical mixers is well known in the field of gas transfer. As the gas bubbles are released into the liquid phase through one of the liquid-gas mixing vessels, only a small fraction of gases becomes soluble in the liquid. The remaining large fraction of gases remains in gaseous form and forms large gas bubbles (over 250 microns in diameter) in the liquid because of gas diffusion created by shearing forces under mainly atmospheric pressure.
Accordingly, at a conventional activated sludge sewage treatment plant, the oxygen transfer efficiency from gas phase into liquid phase is less than 50 percent because diffused coarse air bubbles are supplied to the plant's aeration basins.
At a water softening plant, a swarm of diffused coarse carbon dioxide bubbles are supplied to the recarbonation process unit, again under atmospheric pressure, for precipitation of excessive soluble calcium ions, but only a small amount of carbon dioxide bubbles are chemically effective; the remaining carbon dioxide bubbles are wasted into the ambient air. The bubbles cause no short-term problems, but are contributing to undesirable global warming, the so-called greenhouse effect, in the long run.
Ozone gas is an excellent disinfectant as well as an oxidation agent which is commonly introduced into a liquid stream through a diffuser under nearly atmospheric pressure or negative pressure. This is the well known ozonation process. Any excessive ozone gas escaped from the liquid stream due to poor dissolution contributes to air pollution and also represents an unnecessary waste.
Diffused air flotation, dispersed air flotation, froth flotation, and foam separation are all conventional adsorptive bubble separation processes, in which coarse air bubbles (with a diameter much greater than 250 microns) are generated under nearly atmospheric pressure in one of the liquid-gas mixing vessels. A swarm of coarse air bubbles amounting to 400 percent of the liquid's volumetric flow creates turbulence in the liquid stream, and also provides a large air-to-liquid interface area that allows soluble surface active substances to be separated from the original liquid phase and form a foam or froth phase on the liquid surface.
Dissolved air flotation is an innovative adsorptive bubble separation process, in which extremely fine air bubbles (with diameter less than 80 microns) are required for separation of mainly insoluble suspended solids from the original liquid phase into a thickened scum phase on the liquid surface. The ratio of air volume to liquid volume is only about 1 to 3 percent.
In order to facilitate the aeration, recarbonation, ozonation and dissolved air flotation processes, generation of extremely fine gas bubbles is required, and can be effectively done under high pressure (2 to 7 atmospheric pressures) by the present invention.
Prior apparatus for a compressed air operation is described in U.S. Pat. No. 1,677,265 issued Jul. 17, 1928 to Jens Orten Boving, which relates to liquid pumps of the air-lift type, i.e. of the type in which the liquid is raised in an uptake or ascension pipe by means of compressed air admitted to the pipe at or near its lower end. This patent is particularly directed to an air-lift pump using compressed air still in gaseous form, rather than to a pressure vessel for air dissolution as is the case of the present application. However, it is important to illustrate the development of the air compression art leading to the present disclosure.
A prior apparatus for a compressed air operation applicable to aeration of activated sludge in a sewage treatment plant is described in U.S. Pat. No. 1,937,434 issued Nov. 28, 1933 to William M. Piatt. This patent is particularly directed to an improved compressed air diffusion using a liquid-gas mixing vessel of porous gas diffusion tubes and porous gas diffusion plates. Coarse air bubbles form an upward or horizontal swirling pattern in the liquid in an open tank under normal environmental pressure, and total vessel volume is the summation of liquid volume and gas bubble volume. The present invention utilizes a multi-stage pressure vessel for total dissolution of more than one type of gases (not for distribution and generation of air bubbles) under high pressure ranging 2 to 7 atm. The total pressure vessel volume of the present invention is equal to the liquid volume, and there is no gas flow out of the pressure vessel.
Apparatus for stirring up farinaceous materials in receptacles of any kind by compressed air or other compressed gas is shown in U.S. Pat. No. 1,971,852 issued Aug. 28, 1934, to Paul Goebels. This 1934 patent discloses an improved mixing device using both porous plates and porous tubes for mixing of substances in a container under normal atmospheric pressure of 1. The present invention, however, discloses an improved gas dissolution pressure vessel for soluble gas dissolution under high pressure and high rotation velocity, dissolving either compressed gas or noncompressed gas in liquid and eliminating gas bubbles after entering the pressure vessel. The Goebel's patent relates to an apparatus using compressed air or other gases for mixing purposes and the air or other gases becomes gas bubbles after passing through the porous diffusion media.
Still another apparatus for diffusing gases through porous media is shown in U.S. Pat. No. 3,118,958 issued Jan. 21, 1964, to John W. White. Specifically, White's patent relates to an improved apparatus for continuous production of cellular products which incorporates a micro-porous plate through which a gas is passed in uniform and correct amounts into the material to be formed, and the gas remains in gaseous form. The present invention relates to an improved apparatus for continuous complete dissolution of gas into liquid under pressure, and the gas is no longer in gaseous form in the pressure vessel and continuous formation of micro bubbles with a pressurized water release assembly, instead of with porous media.
Still another apparatus for diffusing gases through porous media is shown in U.S. Pat. No. 3,400,818 issued Sep. 10, 1968 to Gusztav Tarjan. This patent discloses a froth flotation cell which is provided a static vortex inducer unit to which is fed a slurry of material to be separated and air to be dispersed therein, under normal environmental pressure forming a swarm of coarse bubbles. The present invention discloses a multi-stage pressure vessel in which more than one gases are dissolved in liquid, forming no bubbles, no foams, and no froths, in the pressure vessel, and also discloses a pressurized water release assembly for formation of micro bubbles by depressurization, not by gas diffusion.
The method and apparatus for mixing ozone with water in an ozonation process is disclosed by Stuart W. Beitzel et al in their U.S. Pat. No. 3,775,314 issued Nov. 27, 1973. Their patent discloses a new technology by which a whirling mass of fluid in a high pressure zone is injected into a body of water to be purified. The body of water has a pressure lower than that in the high pressure zone, thereby creating in the body of water a partial vacuum zone containing water and water vapor. Introducing ozone and/or oxygen gas at a pressure of less than about 15 psi into the partial vacuum zone, causes the formation of bubbles of the gas in the water. The present invention relates a pressure vessel which completely dissolves ozone and/or oxygen in highly pressurized water at 30-100 psi.
Many U.S. Pat. (No. 3,820,659 issued to Parlette in June, 1974; No. 4,022,696 issued to Krofta in May, 1977; No. 4,303,517 issued to Love et al in December, 1981; No. 4,377,485 issued to Krofta in March, 1983; No. 4,626,345 issued to Krofta in December, 1986; and No. 4,673,494 issued to Krofta in June, 1987) disclose water and wastewater treatment apparatus using dissolved air flotation. While the dissolved air flotation process requires extremely fine air bubbles to increase its treatment efficiency, these patents disclose only improved flotation cells without enclosures (i.e. under normal pressure), but do not disclose any enclosed pressure vessel for dissolved air flotation process optimization. The present invention relates an improved apparatus and method for complete dissolution of various gases for specific optimization applications: ozone for ozonation, carbon dioxide for recarbonation, air for both aeration and dissolved air flotation, and oxygen for oxygenation. In each application, the apparatus disclosed in the present invention produces extremely fine gas bubbles with diameters less than 80 microns.
An apparatus for dissolving a gas such as air into a liquid, under normal one atmospheric pressure, utilizing a submerged tube provided with a means for injecting the gas into the lower end thereof and for inletting liquid into the tube at various locations throughout the length thereof is disclosed in U.S. Pat. No. 4,215,081 issued Jul. 29, 1980 to Kirtland H. Brooks. The applications of Brook's patent and of the present invention are both for dissolving gas. However, the Brook's patent relates to a gas dissolving apparatus without any porous tubes or plates, and being operated under normal one atmospheric pressure for partial gas dissolution due to the fact that a majority of gas remains in gaseous form as bubbles. The present invention relates to an improved gas dissolving method and apparatus being operated under 2 to 7 atmospheric pressure for total gas dissolution, without forming gas bubbles in the pressure vessel.
An apparatus for removing foreign matter form the top surface of water, for use with aquaria, which comprises a discharge tube stationarily disposed in the aquarium and having its upper opening rim below the water surface, is disclosed in U.S. Pat. No. 4,333,829 issued Jun. 8, 1982 to Gerhard Walther. Specifically, Walther's patent relates to an apparatus using coarse bubbles generated by porous media for removing foreign matter under normal pressure. The pressure vessel disclosed in the present invention are used to dissolve gas, not under normal pressure and not for coarse bubble generation. The pressurized water release assembly disclosed in the present invention is for depressurization, and generation of extremely fine micro bubbles without the use of any porous media.
Another prior apparatus for froth flotating is described in U.S. Pat. No. 4,735,709 issued Apr. 5, 1988 to Donald E. Zipperian. This patent discloses a froth flotation system for separating a mineral fraction from an aqueous pulp containing a mixture of mineral and particles. It is accomplished by bubbling gas bubbles into the pulp in an open vessel under normal environmental pressure by two different means that diffuse compressed gas through porous micro diffusers for bubble generation and, in turn, for froth generation. The present invention relates to a pressure vessel in which gas is totally dissolved (i.e. not for bubble formation) under high pressure and over 2,500 rpm rotation velocity. Besides, no froth is involved in the present invention.
Still another prior apparatus for froth flotation is described in U.S. Pat. No. 4,838,434 issued Jun. 13, 1989 to Jan P. Miller et al. Their patent also discloses a froth flotation system in which porous plates are used for bubble generation and froth formation under normal environmental pressure, and in which a tangential inlet is wide open for influent flow coming in by gravity. The present invention relates to a pressure vessel for bubble elimination (i.e. total gas dissolution) under extremely high pressure and over 2,500 rpm rotation velocity, and also relates to a pressurized water release assembly, an open vessel, a chemical mixing chamber, sludge removal means, air emission means, feeders, pumps, etc. for liquid treatment.
Theories and principles of oxygenation, ozonation, aeration, gas dispersion and bubbles generation are fully disclosed by Wang (U.S. NTIS No. PB83-127704-AS, Sept., 1982), and Krofta and Wang (Journal American Water Works Association, Vol. 74, No. 6. P. 304-310, June, 1982). The oxygenation and ozonation system disclosed by Wang (U.S. NTIS No. PB83-127704-AS, Sept., 1982) relates to a hyperbaric reactor vessel into which both oxygen and ozone gases are pumped and diffused together through the same porous plate for simultaneous chemical reaction. The hyperbaric reactor vessel is 50 percent full of liquid, and 50 percent full of compressed gases. The gas transfer inside of said hyperbaric reactor vessel is accomplished by a recirculation pump which sprays the liquid into the compressed gas phase. The present invention is an improved oxygenation and ozonation system into which both oxygen and ozone gases are distributed separately into a pressure vessel for chemical reactions. The present inventors' pressure vessel is full of liquid in which gases are soluble. The total dissolution of the gas inside of the pressure vessel is accomplished by the improved nozzle assembly that gives over 2,500 rpm of rotation velocity. In addition, the present invention involves the use of separate means for dissolution of different gases at desired looations for desired chemical reactions. In an improved liquid treatment plant, air, ozone and carbon dioxide gases are dissolved in the present inventors' pressure vessel at different feed locations inside of the pressure vessel for individual chemical reactions; subsequently, the pressure vessel's effluent is discharged into a flotation clarification tank (i.e. an open vessel) through an improved pressurized water release means for generation of extremely fine oxygen, nitrogen, ozone, and carbon dioxide bubbles. For water purification, chemicals are dosed to the present invention for chemical reactions, coagulation, precipitation, flocs formation, clarification, disinfection, corrosion control, etc. For wastewater treatment, both microorganisms and chemicals are dosed to the present invention for nutrient supply, pH adjustment, bio-oxidation, nitrification, denitrification, phosphate removal, etc.